Pyrolysis of ricinoleates



United States Patent 2,807,633 PYROLYSIS or RICINOLEATES Georges Wetroif, Le Thillay, and Georges DIvachetf and Jean Khaladji', Paris, France, assignors to Organics, S. A., Paris, France No Drawing. Application October 25, 1955,

) Serial No. 542,768

This invention consists in a process for treating ricinoleic acid and its esters to produce high yields of undecylenic acid or its esters and n-heptaldehyde.

Ricinoleic acid and its esters are obtained generally from castor oil which consists chiefly of the glyceryl ester, ricinolein. It has long been known that by subjecting the acid or its esters to elevated temperatures, ricinoleates may be caused to split to yield undecylenates and n-heptaldehyde. The yield of these products, however, may be quite low since numerous other reactions may also occur during the pyrolysis, such as internal dehydration leading to the formation of polyethylenic compounds. In addition, heptylaldehyde and undecylenic acid or its ester are subject to further decomposition upon exposure to high temperatures for excessive periods of time. Because of side reactions of this type, high yields of the heptaldehyde and undecylenate are not generally attained. V

By means of the present invention, the yields of these products are greatly improved and undesirable secondary reactions by which less-valuable by-products would be formed are largely suppressed. In addition, the process is easily and inexpensively carried out.

In general, the process of this invention consists in subjecting ricinoleic acid or its esters to pyrolysis while in admixture with water vapor, the presence of which has been found to enhance the yields of the aldehyde and undecylenate.

The manner in which the presence of water vapor affects the pyrolysis process is not precisely known, but it is suggested that it serves at least in part as a diluent, as a heat reservoir and as an inhibitor of thermal dehydration, it being one of the products of dehydration, according to LeChateliers principle. A further advantage of carrying out pyrolysis in the presence of water lies in its fire retardant nature which eliminates the danger of combustion or explosion.

For best results, the process is carried out by combining the water vapor, generally in theform of superheated steam, with the acid or its esters in the vapor phase or in a liquid phase finely dispersed in the steam, and heating the mixture to a temperature. between about 500 and 700 C. for a short period of time, generally less than 5 seconds and frequently as short as a tenth of a second. The water vapor may be present in any amount practical and improved yields will be obtained, but for best results, the water should be present in an amount in excess of about half the weight of acid or ester. When lesser amounts are present, the yields are lower. At water: ricinoleate ratios above about 0.5 :1 (by weight) the presence of additional water is generally beneficial, but the improvement in yield is relatively little, and at waterricinoleate ratios above 2 the improvementrealized by additional water is so slight that the use of it'is hardly justified under present economic conditions, considering the heat lost in the unproductive heating of the water vapor. Thus preferably, the process is carried out with the water present in an'amount of between about 0.3 and about 3.0 times the weight of the acid or ester, with optimum conditions established in the range of 0.5 and 2.0 parts of water per part acid or ester.

During the pyrolysis phase it has been found to be quite important that the water and ricinoleate vapor be thoroughly mixed and inter-dispersed, and for this purpose the ricinoleate (acid or ester) is advantageously vaporized or dispersed in a stream of water vapor which is then passed to a heating zone. Alternatively, however, the ricinoleate may be dispersed directly into a stream of steam superheated to an extent such that pyrolysis conditions are established When the steam and ricinoleate reach thermal equilibrium, but this requires higher amounts of waterthan are otherwise necessary, and a steam temperature in the neighborhood of 900 C. when.

a ricinoleate at room temperature is dispersed in the steam. Preferably, the steam and ricinoleate are mixed at a temperature of SOC-450 C.,.and the mixture then heated to pyrolysis temperature in a. separate zone.

The yield of undecylenic acid and n-heptaldehyde de-' pend generally upon the time of exposure, the water content, the temperature of pyrolysis, and the particular ricinoleate used. As a general rule, lower temperatures r are required when the esters of lower aliphatic alcohols,

e. g. methyl, ethyl, n-propyl and isopropyl are used than When either an ester of a higher alcohol or the acid itself is used as the raw material. Also, the higher the moisture content, the higher may be the temperature without causing undesirable decomposition of the product. In this connection, it is pointed out that two factors are of paramount importance. High conversion of the ricinoleate to n-heptaldehyde and undecylenate is desired, and this is favored by high temperature. On the other hand, decomposition of the reaction products, also favored by high temperatures, is to be avoided. A high moisture con tent within the range suggested, permits high temperatures favoring high conversion of ricinoleate, while suppressing the undesirable decomposition reactions which would otherwise attend upon a high temperature. The same general considerations apply to the time of the exposure. The invention thus permits operating under conditions of high yield while avoiding the undesirable effects of such conditions.

In heating the mixture of the ricinoleate and the water vapor it is generally sufiicie'nt to conduct the mixture through a chamber to which heat is applied by any conventional means, to maintain the chamber within the temperature range. Best results are attained if the surface by which heat is transferred to the mixture is made as large as practicable so that the rate of heating may be as rapid as possible. For this purpose, the heating zone may be filled with conductive materials presenting an extended heat transfer surface, such as balls or otherv pieces of steel, graphite or other comparable material, or. by utilizing a hot liquid, such as molten lead, through which the.

mixture is bubbled. The desired temperature may in this manner be attained rapidly and local overheating which may result in undesirable cleavage products is avoided.

As the process is preferably carried out, about of the ester or acid treated is utilized, there remaining in the product about 10% unconverted ester which may readilybe collected and recycled. Overall yields from a kilogram of castor oil are typically 280 grams of n-heptaldehyde and upwards of 400 grams of undecylenic acid, particularly when the castor oil is preliminarily converted to methyl ricinoleate, as by conventional alcoholysis, and that ester is subjected to pyrolysis in accordance with this invention.

The products from the reaction zone are preferably condensed rapidly and separated from the water in them by decantation and are then fractionated under reduced pressure. The forerun will generally consist of a small'quantity of by-products of low molecular weight. Following this, the heptylaldehyde, and then the undecylenate distill over. The final distillation residue remaining may then be treated to recover unreacted ricinoleate.

A particular. advantage of carrying out pyrolysis of ricinoleates in this manner lies in the high purity of the products which may be obtained by simple distillation of the reaction products. Ordinarily, the heptaldehyde fraction is 9095% pure and the undecylenate fraction may be collected as practically 100% pure.

The undecylenate ester thus obtained will ordinarily bettreated by hydrolysis to yield the acid which is obtainable ina remarkably pure state.

The examples given below show several representative processes which will give a better understanding of the invention. They are given as illustrative of the invention and are notintended to limit its scope. The methyl ricinoleate containing 8082% ester which is the raw material iri th e first few examples is obtained by alcoholysis of commercial castor oil. As the weight of crude ester obtainedis equal to the weight of oilused, the weight yields which have been indicated pertain both to ricinoleate and to commercial oastor oilwhich is the original raw material in all cases Example 1 The apparatus used'consisted of a vertical steel tube having a height of 100 cm. and a diameter of 6 cm., closed at the bottom and equipped with an inside. tube extending fromthe top to within 10 cm. from the bottom. The outer tube was electrically heated by means of a resistance winding to maintain the temperature within at 575 C.

Technical methyl ricinoleate containing 81.2% ester was injected into the top of the inner tube, after having been dispersed in a current of steam superheated to 350 C. The rate of flow was 1000 g. ester and 1300 g. water per hour. The vapors remained in the furnace 1.5 seconds; their rate of flow was 1.8 liters per second, and they had a linear speed of 0.6 meter per second.

The vapors were collected from the top of the outer tube and rapidly cooled to C. in a refrigerated condenser from which the gaseous by-products were evacuated. The mixture was separated by distillation, after removal of the aqueous layer.

From 1 kg. of crude ricinoleate was obtained:

= G. Loss of uncondensed gaseous products 79 Condensable products oflow molecular weight 51 n-Heptaldehyde containing 90.5% aldehyde 254 Methyl undecylenate containing 99% ester 442 Distillation residues containing 30% ricinoleate 174 Theamount converted in the first passage was The chemical yield was 83% with respect to n-heptaldehyde, 90.5% Wtihrespect to undecylenate.

The residues containing 30% ricinoleate were treated in the. furnace under the same conditions, and the ester contained in them was decomposed with a slightly lower yield, g'ving, after distillation,.l3 g'. of n-heptaldehyde containing 90.5% aldehyde and 23 g. of undecylenate 99% pure.

242g. n-heptaldehyde, i. e. 81.5% of the theoretical amount, and

414 g..undecylenic acid, i. c. 86.5% of the theoretical amount, which is. generally far superior to other. processes,

4 Example 2:

The same apparatus was used, this time'with the tube filled with fused lead to a depth of 40 cm., and maintained at 610 C. by external heating. The vapor-inlet tube was thus immersed in the fused metal to a depth of 30 cm. The raw materials and the flow rates were the same as in the preceding example.

The amount converted in the first pass was the chemical yield of n-heptaldehyde was the same as in Example 1, i. e. 83%, and the yield of undccylenic acid ester was slightly higher, 93%.

Example 3 The furnace in this example was at vertical tube of molybdenum steel having a height of cm. and a diameter of 5 cm., heated from the outside by means of electric resistance coils. The vapors entered the tube at the top and were removed at the bottom. The upper half portion, a preheating zone, was maintained at 400 C., while the lower portion, the reaction zone, washeated to 550 C.

The furnace was filled with Raschig rings, 20 mm. in diameter and height, of the same steel as the walls, in order to increase the contact. surface with the heated metal. Under these conditions, the effective surface area was3000-3500 sq. cm.

The furnace was fed methyl ricinoleate containing 81.2% ester and steam at 350-400" C. by means of an atomizer placed at the top of the tube. The rate of flow was 1500 g. ricinoleate and 2400 g. water per hour.

After the first pass, the following products were obtained from 1 kg. of crude ricinoleate:

G. Loss of gaseous products which cannot be condensed 32 n-Heptaldehyde containing 92.2% aldehyde 199 Methyl undecylenate 99% pure 327 Residues containing 60.3% ricinoleate 411 The amount converted was G. Loss of products which cannot be condensed 97 n-Heptaldehyde 200 Methyl undecylenate 328 Residues containing 13% ricinoleate 305 The suin of the two operations has thus furnished 462 g. of undecylenate 99% pure per kilogram of crude ricinoleate.

The hydrolysis of this ester was carried out with a yield of 88.5% by weight and gave 409 g. of acid melting at 23 C. This represents a total chemical yield of 409 zss of undecylenic acid.

Example 4 V The preceding example was repeated, this time with the furnace heated to a temperature of 590 C. in order to increase the amount of cleavage- In this run, 1 kg. of crude ester yielded:

G. Loss of gaseous products 102 Condensable products of low molecular weight 44 n-Hep'taldehyde containing 96.2% aldehyde 254 Undecylenate 99% pure .438 Residues containing 28.2% ricinoleate 162 The amount converted was Example The experimental conditions were similar to those used in Example 4, but the methyl recinoleate was replaced by isopropyl ricinoleate containing 82% ester. The following products were obtained from 1 kg. of the ester after the first pass:

G. Loss of gaseous products 80 Condensable products of low molecular weight 43 n-Heptaldehyde 96% pure 232 Isopropyl undecylenate 99% pure 465 Residues containing ricinoleate 180 The amount converted The chemical yield was 83.5% based on n-heptaldehyde and 87% based on undecylenate. The acid obtained by hydrolysis of this ester was at a yield of 80% by weight and melted at 23 C.

Example 6 A mixture of castor oil containing 85% ester and steam superheated to 400 C. was passed into a quartz tube of a length of 50 cm. and a diameter of 20 mm. which was filled with small pieces of graphite and heated to 680. The rate of flow was 65 g. of oil and 260 g. of water per hour. After leaving the tube, the products were collected, condensed and cooled to 20 C., and the organic layer was then distilled, after being decanted from the aqueous layer.

From 1 kg. of oil subjected to this treatment, the yield was 265 g. of n-heptaldehyde containing 87% aldehyde. The undecylenic fraction consisting of free acid and its glycerol ester was hydrolized with caustic soda. After being acidified, 320 g. of undecylenic acid melting at 22 C. was collected. Forty grams of acrolein and 13 g. of glycerol were obtained as by-products. The chemical yield was of n-heptaldehyde 76% and64% of acid.

The same experiment was carried out without the introduction of steam and 200 g. of n-heptaldehyde containing 76% aldehyde and 180 g. of impure undecylenic acid were obtained. This represents a yield of n-heptaldehyde of 49% and of low-grade acid of 36%.

Example 7 The furnace consisted of a quartz tube of a length of 1 m. and a diameter of 22 mm. filled with turnings of molybdenum steel. The lower portion, the reaction zone, was heated to 650 C., and was fed with a mixture of steam and technical ricinoleic acid having a titer of 80%. The hourly rates of flow were 50 g. of acid and 125 g. of water. The vapors remained in the reaction zone for 0.2 to 0.3 second and were condensed immediately after leaving it. The organic layer after being separated from the aqueous phase was distilled.

One kg. of crude acid produced: I

G. Volatile produc 112 n-Heptaldehyde 93% pure 213 Undecylenic acid, melting point 23 j 300 Residue free of ricinoleic acid 270 The chemical yield was 64.5% of n-heptaldehyde and 61% of undecylenic acid.

Attempts to carry out the same experiment without steam, resulted in the tube soon becoming clogged, owing to the formation of gums and linoleic resins.

From the foregoing examples and description, it is believed apparent that this invention may be carried out under rather widely varying conditions, and that the specific examples described above may be readily modified by those skilled in the art, Without departing from the scope of this invention. Although it is apparent that either ricinoleic acid or its ester may be treated in the manner described, it will be seen that best results are attained if the raw material ricinoleate is in the form of an ester of a lower aliphatic alcohol, preferably one having no more than four carbon atoms.

We claim:

1. In the pyrolysis of ricinoleates wherein material selected from the group consisting of ricinoleic acid, the lower aliphatic alcohol esters of ricinoleic acid, the glyceryl esters of ricinoleic acid and castor oil is thermally decomposed by being subjected to elevated temperatures to yield n-heptaldehyde and an undecylenate, the improvement comprising subjecting said material to pyrolysis conditions while in admixture with water vapor at a temperature between about 500 C. and 700 C.

2. The method of treating ricinoleates to produce nheptaldehyde and undecylenates comprising heating material selected from the group consisting of ricinoleic acid, the lower aliphatic alcohol esters of ricinoleic acid, the glyceryl esters of ricinoleic acid and castor oil while in admixture with water vapor to a temperature between about 500 C. and 700 C., and cooling the mixture.

3. The method of treating ricinoleates to produce nheptaldehyde and undecylenates comprising heating material selected from the group consisting of ricinoleic acid, the lower aliphatic alcohol esters of ricinoleic acid, the glyceryl esters of ricinoleic acid and castor oil while in admixture with water vapor in an amount greater than about 0.3 part by weight of water per part of said material to a temperature between about 500 C. and 700 C., and cooling the mixture.

4. The method of treating ricinoleates to produce nheptaldehyde and undecylenates comprising heating material selected from the group consisting of ricinoleic acid, the lower aliphatic alcohol esters of ricinoleic acid, the glyceryl esters of ricinoleic acid and castor oil while in admixture with water vapor in an amount of between about 0.5 and 2.0 parts by weight of water per part of said material to a temperature between about 500 C. and 700 C., and'cooling the mixture.

5. The method of treating ricinoleates to produce nheptaldehyde and undecylenates comprising heating material selected from the group consisting of ricinoleic acid, the lower aliphatic alcohol esters of ricinoleic acid, the glyceryl esters of ricinoleic acid and castor oil while in admixture with water vapor in an amount of between 0.5 and 2.0 parts by weight of water per part of said material to a temperature between about 500 C. and 700 C. for between about 0.1 second and five seconds, and cooling the mixture.

6. The method of treating ricinoleates to produce nheptaldehyde and undecylenates comprising heating a ricinoleate ester of a lower aliphatic alcohol having no more than four carbon atoms while in admixture with water vapor to a temperature between about 500 C. and 700 C., and cooling the mixture. 7

7. The method of treating ricinoleates to produce aacid, the lower aliphatic alcohol esters of ricinoleic acid,

the 3 glyceryl" esters ofiricinoleic acid" and caster 'oilgin water vapor superheated toa temperature betweenabout 300 C. and- 450 0., the'arnount of water vapor being in excess of 0:3-partby weight per part of said material, h'eating,the mixture of Water; vapor and material to a temperature between about 500 C. and 700 C. for a period of time less than five seconds and cooling the mixture.

8. The method of treating ricinoleates to produce nheptaldehyde andundecylenates; comprising dispersing materialselected from the group consisting of ricinoleic acid, the lower aliphatic alcohol esters of ricinoleic acid, the glyceryl esters of ricinoleic'acid andcastorxoil in water vapor, the amount of water vapor' being in excessof 0.3 part by Weight per part of said mixture, passing the mixture thus formed into contact with the surface ofa heating zone heated to a temperature between about 500 C.

and 700 Cl, andco oling themixture aftercontact with said surface.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE PYROLYSIS OF RICINOLEATES WHEREIN MATERIAL SELECTED FROM THE GROUP CONSISTING OF RICINOLEIC ACID THE LOWER ALIPHATIC ALCOHOL ESTERS OF RICINOLEIC ACID, THE GLYCERYL ESTERS OF RICINOLEIC ACID AND CASTOR OIL IS THERMALLY DECOMPOSED BY BEING SUBJECTED TO ELEVATED TEMPERATURES TO YIELD N-HEPTALDEHYDE AND AN UNDECYLENATE, THE IMPROVEMENT COMPRISING SUBJECTING SAID MATERIAL TO PYROLYSIS CONDITIONS WHILE IN ADMIXTURE WITH WATER VAPOR AT A TEMPERATURE BETWEEN ABOUT 500*C. AND 700*C. 